UNIX for Dummies Questions & Answers

I ran a tar command on an HP 11.11 box with 12 processors and then ran top. I noticed that the tar command was "jumping" between processors, for example during one iteration of top the tar command would be running on processor 3 and during the next iteration it would be running of processor 7. Can someone please explain the reason/advantage of this? A link would be helpful also. Thanks.

12 cpu's...whoa! Is this a superdome?

tar is i/o bound by nature. It does a read or write and must wait until that completes. It is not running or runable while it's waiting for i/o to finish...therefore it is not in a cpu. When the i/o finishes, the process to put on the run queue. "Idle" cpu's are scanning a run queue looking for something to run. With 12 cpu's you have enough idle cpu's scanning the run queue that there is a good chance the process will get a different cpu.

Some os'es have a processor affinity concept (not sure if HP-UX does). Here, if several runnable processes of equal priority are available, the cpu picks one it recently ran. Almost all os's have a system call to influence proceesor choice, with HP-UX it's mpctl.

One process bouncing among a few cpu's is not too bad. But cpu's will have on-chip (or at least per processor) caches. It's better if processes can be routed to cpu's they previously used.

Thanks for the explanation. To some here it's kind of like a superdome...we like to call it payroll.

hehe I have a single partition superdome, we just upgraded it from 48 to 64 procs running a single 1.4TB instance of oracle and the supporting app as well. And added from ~72GB to ~106GB of memory

CPU Count: 64
CPU Speed: 750 MHz
CPU HW Support: 64-bit
Kernel Support: 64-bit
RAM Size: 106240 MB

64 cpu's in one partition! Must be fun running top...

top -h always!!!